Salts comprising an organic, inorganic or organometallic cation and a nonnucleophilic counteranion have been shown to have utility as photochemically activated initiators for cationic addition polymerization or as similarly activatable latent Br onsted- or Lewis-acid catalysts for step-growth (or condensation) polymerization, depolymerization and unblocking of functionalized polymers. Common commercial photoinitiator salts include onium and organometallic salts such as diaryliodonium and triarylsulfonium salts and (cyclopentadienyl)(arene)iron.sup.+ salts of the anions PF.sub.6.sup.- and SbF.sub.6.sup.-. In certain cases, these same salts may also photoinitiate free-radical addition polymerization and are useful in "dual cure" applications where a mixture of cationically sensitive and free-radically polymerizable monomers arc polymerized either simultaneously or sequentially. Similarly, certain classes of these salts are known to be thermally-activatable curatives for cationic, step-growth and free-radical polymerizations.
For many commercial applications, the polymerizable monomers are multifunctional (i.e., contain more than one polymerizable group per molecule), for example, epoxides, such as diglycidyl ethers of bisphenol A (DGEBA) and vinyl ethers, such as 1,4-cyclohexanedimethanol divinyl ether (CHVE). Mixtures of multifunctional monomers such as polyisocyanates and polyalcohols (polyols) or polyepoxides and polyalcohols can undergo acid-catalyzed polycondensation via a step-growth mechanism. Also included in this description are multireactive monomers- those that comprise two or more classes of reactive groups, such as, for instance, a monomer comprising both acrylate and isocyanate functionalites.
Compounds and materials comprising charged ions (i.e., salts) tend to have poor solubility in many organic solvents. As many useful types of compositions are based on organic systems, either organic polymer systems or organic monomer systems, reduced solubility in organic systems limits the field of utility of many ionic materials. Amongst the ionic materials that could benefit from increased solubility in organic systems are polymerization initiators (particularly those based on iodonium, sulfonium, diazonium, phosphonium and organometallic complex cations).
Synthetic modifications of the cationic portion of cationic initiators have been made to improve their solubility in organic systems. However, the difficulty and cost of introducing solubilizing substituents has limited commercial application of these materials. Alternatively, the use of reactive diluents or solid dispersants has also been disclosed.
In many applications photoinduced polymerization is impossible, impractical or undesirable. For example, many situations where polymerization reactions occur in a closed environment (i.e., in a mold or in a laminated product) or where polymerizable compositions may contain opacifying pigments, thermally activated initiators are preferred. Thermally-activated initiators, such as known onium or organometallic salts may initiate polymerization at ambient or higher temperatures depending upon the specific application. Additional additives, such as oxidants, reductants, metal salts, alcohols, organic acids or anhydrides, and. combinations thereof are frequently added to control the temperature at which cationic polymerization will occur.
In addition to known onium or organometallic salts, ammonium salts and metal salts of fluoroalkanesulfonic acids and bis(fluoroalkylsulfonyl)methanes have been used as thermal initiators for cationic addition polymerization of vinyl ethers and epoxies or catalysts for alcohol-epoxy step-growth polymerization.
The nature of the counteranion in a complex salt can influence the rate and extent of cationic addition polymerization. For example, J. V. Crivello, and R. Narayan, Chem. Mater., 4, 692, (1992), report that the order of reactivity among commonly used nonnucleophilic anions is SbF.sub.6.sup.- &gt;AsF.sub.6.sup.- &gt;PF.sub.6.sup.- &gt;BF.sub.4.sup.-. The influence of the anion on reactivity has been ascribed to three principle factors: (1) the acidity of the protonic or Lewis acid generated, (2) the degree of ion-pair separation in the propagating cationic chain and (3) the susceptibility of the anions to fluoride abstraction and consequent chain termination.
Bis(perfluoroalkylsulfonyl)methides (e.g., U.S. Pat. Nos. 4,039,521; 4,049,861; 4,069,368; 4,100,134; 4,115,295, and 5,136,097) and bis(perfluoroalkylsulfonyl)imides (e.g., U.S. Pat. Nos. 4,031,036; 4,387,222; 4,247,674; 4,429,093, ) have been used as anions for catalysts and initiators. Improvements in the use of those anions and their synthesis have been described in the literature, see for example U.S. Pat. Nos. 3,704,311; 3,758,531; 3,758,591; 3,758,952; and 3,758,953; and J. N. Meussdorffer, et al., Chem. Ztg., 1972, 38, p.582.
The thermal decomposition chemistry of a tris-(perfluoromethylsulfonyl)methide salt of benzene diazonium cation was studied and reported by both Y. L. Yagupolskii, et al., J. Org. Chem. U.S.S.R. (Engl. Transl.), 1990, 26, 584-5; and S. Z. Zhu, et al., Inorg. Chem., 1993, 32, pp. 223-226. Additionally, Zhu studied the thermal decomposition chemistry of the bis(perfluoromethylsulfonyl)imide salt of a benzene diazonium cation, although no catalytic activity for these salts was described.
U.S. Pat. No. 4.049,861 discloses the use of certain classes of catalysts in the curing of epoxide resins and silane resins, including highly fluorinated alkylsulfonyl methanes. A single tris-perfluoroalkylsulfonyl methane is shown on col. 8, line 38, and the class is within the generic formula on column 7. Similarly, U.S. Pat. No. 4,115,295 describes a single tris (perfluoroalkylsulfonyl) methane on column 7, line 11.
U.S. Pat. No. 4,920,182 and 4,957,946 describe energy-polymerizable compositions comprising arene-iron salts of, e.g., fluoroalkylsulfonic acid (fluoroalkylsulfonates). U.S. Pat. No. 5,089,536 describes energy-polymerizable compositions comprising organometallic salts as initiators. Numerous anions are disclosed as being suitable counterions for the organometallic cations disclosed therein.
Co-assigned PCT Patent Application No. 95/03338 describes organometallic initiator salts comprising, aryl borate anions, e.g., tetrakis [3,5bis(trifluoromethyl)phenyl] borate. These non-nucleophililc anions provide enhanced reactivity toward cationic addition polymerization as well as improved solubility in organic media. However, the syntheses of such anions tend not to be cost efficient.
Conductive adhesives useful in the electronics field are known. Such adhesives that enable multiple discrete electrical connections, often in extremely close proximity to each other, between two components are commonly referred to as "anisotropically conductive adhesives" or as "z-axis adhesives." A typical use for this type of material is to provide connection between a flexible printed circuit and a flat panel display. U. S. Pat. No. 5,362,421 describes anisotropically conductive adhesives wherein the thermal initiator comprises an organometallic cation and an anion selected from tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, hydroxypentafluoroantimonate, trifluoromethanesulfonate and hexafluoroantimonate.